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当定点设备(通常指鼠标)移动到元素上时就会触发 mouseenter 事件

类似 mouseover,它们两者之间的差别是 mouseenter 不会冒泡(bubble),也就是说当指针从它的子层物理空间移到它的物理空间上时不会触发

mouseenter.png
One mouseenter event is sent to each element of the hierarchy when entering them. Here 4 events are sent to the four elements of the hierarchy when the pointer reaches the text.
mouseover.png
One single mouseover event is sent to the deepest element of the DOM tree, then it bubbles up the hierarchy until it is canceled by a handler or reaches the root.

With deep hierarchies, the amount of mouseenter events sent can be quite huge and cause significant performance problems. In such cases, it is better to listen for mouseover events.

Combined with the behavior of its symmetrical event, mouseleave, the mouseenter DOM Event acts in a very similar way to the CSS :hover pseudo-class.

General info

Specification
DOM L3
Interface
MouseEvent
Synchronicity
Synchronous
Bubbles
No
Cancelable
No
Target
Element
Default Action
None

Properties

Property Type Description
target 只读 EventTarget The event target (the topmost target in the DOM tree).
type 只读 DOMString The type of event.
bubbles 只读 Boolean Whether the event normally bubbles or not
cancelable 只读 Boolean Whether the event is cancellable or not?
view 只读 WindowProxy document.defaultView (window of the document)
detail 只读 long (float) 0.
currentTarget 只读 EventTarget The node that had the event listener attached.
relatedTarget 只读 EventTarget For mouseover, mouseout, mouseenter and mouseleave events: the target of the complementary event (the mouseleave target in the case of a mouseenter event). null otherwise.
screenX 只读 long The X coordinate of the mouse pointer in global (screen) coordinates.
screenY 只读 long The Y coordinate of the mouse pointer in global (screen) coordinates.
clientX 只读 long The X coordinate of the mouse pointer in local (DOM content) coordinates.
clientY 只读 long The Y coordinate of the mouse pointer in local (DOM content) coordinates.
button 只读 unsigned short This is always 0 as no button presses trigger this event (mouse movement does).
buttons 只读 unsigned short The buttons depressed when the mouse event was fired: Left button=1, Right button=2, Middle (wheel) button=4, 4th button (typically, "Browser Back" button)=8, 5th button (typically, "Browser Forward" button)=16. If two or more buttons are depressed, returns the logical sum of the values. E.g., if Left button and Right button are depressed, returns 3 (=1 | 2). More info.
mozPressure 只读 float The amount of pressure applied to a touch or tabdevice when generating the event; this value ranges between 0.0 (minimum pressure) and 1.0 (maximum pressure).
ctrlKey 只读 boolean true if the control key was down when the event was fired. false otherwise.
shiftKey 只读 boolean true if the shift key was down when the event was fired. false otherwise.
altKey 只读 boolean true if the alt key was down when the event was fired. false otherwise.
metaKey 只读 boolean true if the meta key was down when the event was fired. false otherwise.

Examples

The mouseover documentation has an example illustrating the difference between mouseover and mouseenter.

The following example illustrates how to use mouseover to simulate the principle of event delegation for the mouseenter event.

<ul id="test">
  <li>
    <ul class="enter-sensitive">
      <li>item 1-1</li>
      <li>item 1-2</li>
    </ul>
  </li>
  <li>
    <ul class="enter-sensitive">
      <li>item 2-1</li>
      <li>item 2-2</li>
    </ul>
  </li>
</ul>

<script>
  var delegationSelector = ".enter-sensitive";

  document.getElementById("test").addEventListener("mouseover", function( event ) {
    var target = event.target,
        related = event.relatedTarget,
        match;

    // search for a parent node matching the delegation selector
    while ( target && target != document && !( match = matches( target, delegationSelector ) ) ) {
        target = target.parentNode;
    }

    // exit if no matching node has been found
    if ( !match ) { return; }

    // loop through the parent of the related target to make sure that it's not a child of the target
    while ( related && related != target && related != document ) {
        related = related.parentNode;
    }

    // exit if this is the case
    if ( related == target ) { return; }

    // the "delegated mouseenter" handler can now be executed
    // change the color of the text
    target.style.color = "orange";
    // reset the color after a small amount of time
    setTimeout(function() {
        target.style.color = "";
    }, 500);
    

  }, false);
 

  // function used to check if a DOM element matches a given selector
  // the following code can be replaced by this IE8 compatible function: https://gist.github.com/2851541
  function matches( elem, selector ){
    // the matchesSelector is prefixed in most (if not all) browsers
    return elem.matchesSelector( selector );
  };
</script>

Browser compatibility

Feature Chrome Edge Firefox (Gecko) Internet Explorer Opera Safari
Basic support 30[1] (Yes) 10[2] 5.5 (Yes)
未实现 15.0
17.0
7[3]
On disabled form elements 未实现 未实现 44.0 (44.0)[4] 未实现 未实现 ?
Feature Android Chrome for Android Edge Firefox Mobile (Gecko) IE Mobile Opera Mobile Safari Mobile
Basic support ? ? (Yes) ? ? ? ?
On disabled form elements ? ? 未实现 ? ? ? ?

[1] Implemented in bug 236215.

[2] Implemented in bug 432698.

[3] Safari 7 fires the event in many situations where it's not allowed to, making the whole event useless. See bug 470258 for the description of the bug (it existed in old Chrome versions as well). Safari 8 has correct behavior

[4] Implemented in bug 218093.

See also

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